Certain types of calcium phosphate materials are biologically important. For example, apatitic calcium phosphates, hereafter referred to as apatites, are the primary mineral constituent of bone and teeth. Described generally, bone and tooth minerals proceed through a sequence of phases of which the final mineral phase is an apatite similar to hydroxyapatite, see e.g., I. Zipkin, Biological Mineralization (Wiley, 1973). The basic chemical formula of hydroxyapatite (also spelled hydroxylapatite) is Ca.sub.10 (PO.sub.4).sub.6 (OH).sub.2. The actual composition of bone and tooth minerals can vary substantially from this formula. For example, commonly present in the various phases of the mineralized tissues of bones and teeth are calcium-deficient apatite species, carbonate species and various other apatitic species such as fluoroapatite.
Hydroxyapatite is held together primarily by ionic bonding; the calcium ions are divalent cations (Ca.sup.++), the phosphate ions are trivalent anions (PO.sub.4.sup.---), and the hydroxyl ions are monovalent anions (OH.sup.-).
Hydroxyapatite and other forms of calcium phosphate have several advantages when used in repairing bones and tooth enamel. Since they have chemical compositions that are similar or identical to the mineral that exists naturally in bone and tooth enamel, calcium phosphates can be comparable to natural tooth and bone material with regard to numerous important parameters. Such parameters include thermal conductivity, thermal coefficient or expansion, hardness, strength, color, and insolubility in saliva and other acidic or basic solutions. Being thus comparable to natural tooth and bone material, calcium phosphates tend to be relatively biocompatible. As used herein, biocompatibility refers to any combination of characteristics which eliminate or minimize adverse reactions when a substance is implanted in the body. Such materials should not cause antigenic, pyogenic, pyrogenic, or inflammatory responses in the recipient. They should not cause galvanic currents, or be corroded, metabolize or dissolve into undesired substances.
There have been a substantial number of efforts to utilize various forms of apatite and other calcium phosphate materials in the repair and reconstruction of bone and tooth enamel. A number of patents and articles describe the use of hydroxyapatite obtained from marine coral and bone powder. See, e.g., U.S. Pat. Nos. 2,508,816 (bone powder) and 3,929,971 (marine coral).
Such materials often contain various other calcium phosphates, such as whitlockite and brushite.
Several other patents and articles describe synthetic apatite materials. See, e.g., U.S. Pat. Nos. 4,046,858 (Barsa et al, 1978); 4,274,879 (Irvine, 1981); 4,330,514 (Nagai et al, 1982); 4,324,772 (Conn et al, 1982); 4,048,300 (Tomlinson et al, 1977); 4,097,935 (Jarcho, 1978) 4,207,306 (Jarcho, 1980); 3,379,541 (Tuvell, 1968).
Several patents and articles describe methods of treating apatite materials in order to render them suitable for tooth implants and other prosthetic devices. Such techniques usually involve sintering or other methods of heating and compaction which convert powdery material into solid porous articles in various shapes. See, e.g., U.S. Pat. Nos. 4,308,064 (Takami et al, 1981); 4,113,500 (Ebihara et al, 1978); 4,222,128 (Tomonaga et al, 1980) 4,135,935 (Pfeil et al, 1979); 4,149,893 (Aoki et al, 1979); 3,913,229 (Driskill et al, 1975).
Several patents and articles describe the use of techniques such as laser radiation to bond apatite materials to tooth surfaces which have been drilled to remove tooth decay. See, e.g., U.S. Pat. No. 4,224,072 (Steward, 1980); R. H. Stern et al, Optics and Laser Technology, p. 22, February, 1975.
Several patents describe the use of particulate or compacted apatite in conjunction with various other compounds, such as fillers and cements. See, e.g., U.S. Pat. Nos. 4,230,455 (Hidaka et al, 1980); 4,223,412 (Aoyagi et al, 1980); 4,131,597 (Bluethgen et al, 1978).
The materials and methods cited above are likely to perform with varying degrees of success when used to promote the healing or restoration of bones and teeth. However, a need exists for continuing improvements in materials and techniques used to promote the regeneration of repair of bones or teeth.